US2335073A - Pressure actuated switch - Google Patents

Description

y Patented Nov. 23, 1943 PRESSURE ACTUATED SWITCH Erle Martin, West Hartford, and Thomas E. Doherty, 'South Glastonbury, Conn., assignors to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application December 27, 1940, serial No. 311,868

(ci. zoo-s2) 13 Claims.

This invention relates to improvements in hydraulic control devices and has particular reference to an improved control unit for a hydrocontrollable feathering-type propeller.

An object of the invention resides in the cornbination of an improved pressure actuated electric switch for discontinuing the application of pressure to a hydraulic mechanism when the pressure has reached a predetermined value.

A further object resides in the\provision of ai# 10 improved pressure actuated switch of the character indicated which is responsive to a difference in the inlet and exhaust pressures of a hydraulic mechanism such as a propeller pitch changing mechanism.

A still further object resides inthe provlsionl-' of an improved pressure actuated switch' of the character indicated which may be connected into a hydraulic circuit without danger of leakage of hydraulic fluid through or from the switch mechanism and in which the switch contact points are immersed in hydraulic fluid which tends to damp any tendency of the electric current to arc at the contact points.

Other objects and advantages will be more particularly pointed out hereinafter or will become apparent as the description proceeds;

In the accompanying drawing in which like reference numerals are used to designate similar parts throughout,.there is illustrated in two somewhat different forms a suitable mechanical arrangement for the purpose of disclosing the invention. The drawing, however, is for the purpose of illustration only and is not to be taken as limiting or restricting the invention since it will be apparent to those skilled in the art that various changes in the illustrated construction may be resorted to without in any way exceeding the scope of the invention.

In the drawing,

Fig. 1 is a schematic partly sectional view of a hydro-controllable feathering-type propeller.

Fig. 2 is a schematic view of the control apparatus for such a propeller schematically illustrating the manner in which a pressure actuated switch such as that constituting the invention is incorporated therein. f l

Fig. 3 is a detailed sectional view on an enlarged scale of a pressure actuated switch constructed according to the invention, the switch being shown in operative position with respect to a member of the control apparatus through whichfiuid conduits extend, and

tuated'switch constructed according to the invention.

Referring to the drawing in detail, the numeral I 0 generally indicates a propeller driving shaft projecting from an engine generally indicated at I2 and carrying a hydro-controllable featheringtype propeller generally indicated at I4. This propeller may be of the type particularly illustrated and described in my co-pending United States application Serial No. 184,792, filed January 13, 1938, for Feathering propeller control, and may have a hub I6 carrying a plurality of blades, one of which is indicated at I8, rotatably mounted therein for pitch changing movements.

Each blade may be provided with a gear member 2|) all of which mesh with a gear 22 carried by a V rotatable cam member 24 which is in turn supported in a fixed cam member 26 for changing the pitch of the propeller blades. The cam 24 may be rotated by means of a piston 28 reciprocable in a relatively fixed cylinder 30 and carrying cam followers as particularly illustrated andV described in `United-States application Serial No. 184,792, re-

-ferred to above. Hydraulic fluid is led to a passage 32 in the shaft III from a suitable conduit 34 and .oil transfer bearing 36 and hydraulic fluid from a different source is also led to a conduit 38 within the propeller shaft through a tubular connection40. Both of the passages 32 and 40 lead Fig. 4 is a detailed sectional view on an enlarged to a valve generally indicated at 42 which, when subjected to pressures below a predetermined limit, connects the passage 32 with the interior of the cylinder 30 at the pitch increasing side of the piston 28 and connects the passage 38 with the interior of the cylinder 30 at the pitch decreasing side of the piston. This position of the valve 42 is shown in Fig. 1. When subjected to pressures above the above mentioned predetermined llmits the connection of these passages to the respective ends of the cylinders is reversed. The passage 32'is then connected to the interior of the cylinder at the pitch reducing side of the piston 28 while the passage 38 is connected to the interior of the cylinder at the pitch increasing side of the piston. Within the shaft I0 the passages 32 and 38 are separated and the end of the passage 32 is closed by a suitable plug 44 disposed in the bore of the shaft, Referring now to Fig. 2 it will be observed that the conduit 34 leads to the outlet side of a governor, generally indicated at 48 and the passage 38 is connected by the conduit 4U with a pump 48 which may be the engine oil supply pump the outlet pressure of which is controlled by the pressure relief valve 50. From the pump outlet conduit 40 a passage 52 leads to the engine lubricating system and a passage 54 leads to the governor 46. This governor may include a booster pump and a governor actuated valve disposed between the outlet of the booster pump and the passage 34 which construction is particularly illustrated and described in United States Patent No. 2,204,640, issued June 18; 1940, to Elmer E. Woodward for Governor mechanism.

With the arrangement so far described it is apparent that Voil at engine lubricating oil pressure will be continuously supplied to the interior of the cylinder 30 at the pitch decreasing side ci the piston 28 while oil from the governor, at a pressure controlled by` the governor booster pump, will be supplied to the cylinder 30 at the pitch increasing side of the piston 28 under the control of the governor actuated valve which acts to connect the space at the pitch increasing side of the piston with the outlet of the booster pump or with a drain, presently to be described, as the governor demand for a change of speed may require. As is clearly set forth in my co-pending United States application Serial No. 184,792, referred to above, the pitch changing mechanism is provided with some form of intermediate pitch limit stop which will prevent the mechanism from turning the blades beyond a predetermined high pitch position when actuated by hydraulic fluid at the pressure supplied by said governor booster pump to keep the pitch within the range of constant speed control.

When it is desired to bring the propeller to a feathered position high pressure fluid from any suitable source is supplied to channel B and preferably electrically controlled. In the structure chosen for disclosing the invention a motor 56 is energized to drive a high pressure pump 58 the outlet of which is connected through a channel E0 with a valve 62 which acts, when subjected to high pressure fluid from the pump 58 to block olf the governor outlet channel 64 and connect the channel 34 directly with the outlet of the pump 58 to supply hydraulic fluid at the increased pressure, sufficient to override the intermediate pitch limit stop mentioned above, to the space within the cylinder 30 at the pitch increasing side of the piston 28 to rotate the propeller blades to their limiting high pitch or feathered position.

Energization of the motor 56 is controlled by a relay switch 66 interposed in the circuit between the motor and the source of power such as the battery 68. This relay switch is urged toward its open position by a spring 'l0 and is closed by a solenoid 12 the energization of which is controlled by a manually operable switch 14. Switch 14 is urged toward its open position by a spring 16 and retained in closed position by a solenoid 18 the energizing circuit of which includes the pressure operatedrswitch 80 hydraulically connected with the channel 60 in such a manner that fluid pressure in the channel 60 at a predetermined value will open this switch. Opening of switch 80 de-energizes the solenoid 18 and permits switch 14 to open under the influence of the spring 16 thus de-energizing the solenoid 12 and permitting the relay switch 66 to open under the influence of the spring 10. Opening of switch 86 de-energizes the motor B and stops the pump 58. The predetermined pressure value selected is a value slightly above the maximum required to turn the propeller blades in a pitch increasing direction between intermediate high pitch position and feathering position indicating that the propeller has reached its full feathered condition.

Since the pressure necessary to feather the propeller is not always the same, varying somowhat with the viscosity of the hydraulic fluid and the resistance met'by the fluid exhausted from the space at the pitch decreasing side of the piston it has been found desirable to connect the space at the side of the switch actuating member opposite the space at the side connected with the channel 60 to the channel 40 through which the fluid vents from the pitch decreasing end oi the cylinder 30. Such a fluid connection is indicated at 8l. This arrangement causes the pressure actuated cut-out switch to operate on the difierence between the pressure of the fluid supplied to the pitch increasing side of the pitch changing mechanism and the pressure of the fluid vented from the pitch decreasing side of the mechanism when the propeller is brought to its feathered position which arrangement gives a more sensitive action of the switch and insures that the propeller will have reached a fully feathered condition before the feathering circuit is broken by the switch 80.

It has been assumed that the switch shown in Fig. 2 is of the same form as the switch shown in Fig. 3 which has been generally designated by l,the numeral 80 while the somewhat modified form of switch shown in Fig. 4 is generally designated by the numeral 80.

The switch B0 comprises a casing 82 which may be conveniently formed as a metal casting or forging. This casing has a flat plate 84 for cooperation with the flat face of a pad 86 to which the switch is attached, a gasket 88 being preferably included between the switch and the pad to prevent leakage of fluid through this joint. The pad B6 is formed integrally with some portion of the control apparatus, for example with the base or pad 90 of the governor 40 and the switch is secured to the pad by suitable means such as the screws 92. Within the casing B2 there is a cylindrical bore 94 having a reduced cylindrical extension 96 at one end thereof the end of which is closed by the wall of the casing and having an internally screw threaded portion 58 at the opposite open end thereof. An insulating bushing |00 is molded onto a plunger' |02 and positioned in the reduced extension 96 of the cylindrical bore. The plunger |02 carries a contact portion |04 and extends through this bushing to a position near the closed end of the extension 96. A second contact member |06 is secured in the closed end of the extension 94 in position to cooperate with the contact member |04 and is connected with a return to the battery B8 which may be through the ground indicated at |08. At its end opposite the contact member |04 the plunger |02 projects into the chamber ||0 formed by the inner portion of the bore 94 and carries an abutment ||2 for one end of a compression spring ||4 the opposite end of which bears against an abutment ||6 formed on the inner end of a connector ||8 fixed in a terminal member |20 by a bushing |22 of insulating material. The terminal member |20 is provided with an externally threaded portion which cooperates with the threaded portion 98 of the bore 94 and with a shoulder |24 which provides a nut for turning the member |20 and also cooperates with the gasket |26 to provide a seal between the member |20 and the casing 82. It is to be understood, however, that the terminal member may be secured to the casing by other suitable `membr-irs |84 and |05.

means such, for example. as flange bolts or a gland nut. The channel lv leads into thechamber iii! and the channel t is led to the space at the closed end of the cylindrical extension 96 ol the bore 94 which space contains the contact The bushing .|00 is preierably `formed of insulating material. such as a thermo-setting phenolic condensate and is dimensioned to provide a positive clearance between itself and the wall of the/bore 96 so that a small quantity of the i'iuidiorced under pressure into the space between the inner end of this bushing and the closed end of the bore will pass into the chamber ||0 denned by the larger bore S4, and into the drain channel 8| to prevent accumulation of sludge and congealing of o-l in the contact chamber` The spring ||4 is sufficiently resilient to permit separation of the contact members .|04 and |05 when the pressure of the iluid in the Space at the closed end of the bore reaches the selected value at which the circuit through the pressure switch is to be broken. When the pressure of the uid in the space containing the contact members |04 and |06 reaches the value indicated these `embers will be separated breaking the circuit and de-energizing the ieathcring pump motor.

While the electrical-contact between the members |02 and ||8 is shown to comprise the spring H4 it is to be understood that an additional flexible electrical conduit can be secured between these two members if desired,

In the slightly modied form of the invention shown in Fig. 4, the casing |28 is substantially the same as the casing 82 of the switch shown in Fig. 3 and has an internal bore |30 with a cylindrical extension |32 at one end thereof the end of the extension being closed bythe end wall of the casing. At the open end of the bore casing is provided with a cylindrical extension i. |34 having external screw threads for the recep-v tion of the internal screw threadsin the end of a terminal member |36. This terminal member is provided with an internal shoulder |38 which engages the edge of a circumferential flange provided on a sealing member` |40 which carries the connecting plug H8. The body portion of the sealing member |40 is dispo-sed within the cylindrical portion |34 of the casing |28 to pro-y vide a hrm support for the member in the casing. Witl'i this arrangement seal member |40 can be independently removed from the casing when the terminal member |36 has been removed. The

- factoring standpoint.

extension |32 contains a resilient bushing |42 of v some suitable material .such as rubber or syn-` thetic rubber and through this bushing extends a stem M4 similar to the stem |02 and carrying a contact member |46 which cooperates with a contact member |48 secured in the end wall of the casing. A spring |50 extends between suitable abutments carried respectively by the members H8 and- |44 and, if desired, a liexible electrical conduit may be connected between these members. A channel |52 leads to the space containing the contact members |46 and'MB and a channel |54 leads into the chamber containing the spring |50, the channel |52 being arranged lor connection with the high pressure channel |50 in the governor base and the channel |54 being arranged for connection with the lowV pressure channel 8| in the governor base in the manner described above.

The switches shown in Figs. 3 and 4 both operate in the same manner, the structural dierences shown in these two embodiments of the invention being mainly important from a manu- In the switch mechanism shown in Fig. 3 the sealing member |22 is molded into the terminal member |20 around the internal shoulder |56 `and the connecting plug ||8 which means thatthe terminal member and the connecting plug both have to be at hand when the molding or vulcanizing process is performed and that the three members namely the terminal |20, the bushing |22 and the connecting plug I8 constitute a single unit when the bushing has been v formed in place. In the form shown in Fig. 4 the seal member or bushing |40 can be made separately and thereafter the connecting plug ||8 can be inserted through an aperture in the bushing and riveted in place and the unit comprising the bushing |40 and connecting plug ||8 can be assembled with the switch when the terminal |36 is screwed into place on the cylindrical extension of the casing, In this case the terminal |36 and connecting plug ||8 do not have to be incorporated in the structure during the molding or vulcanizing process and these various units can be brought together and assembled by the manufacturer or user of the switch.

While two slightly different mechanical arrangements have been hereinabove described and illustrated in the accompanying drawing it is to be understood that various other structural modiiications may be resorted to without in any way changing the method of operation of the switch or exceeding the scope of the invention so long as the structure provides that the make and break contact members are immersed in hydraulic fluid at thc time they become operative to interrupt the circuit including this switch. While it is desirable that the switch operate on the difference between the high pressure and the low pressure sides of the hydraulic mechanism, it is within the scope of the invention that the switch should operate only on the pressure of the high pressure side.

While a suitable mechanical embodiment in two somewhat different forms has been hereinabove describcdand illustrated in the accompanying drawing for the purpose of disclosing the invention, it is to be understood that the invention is not'limited to the particular embodiment so described and illustrated, but thatV- such, changcsin the size, shape and arrangement of the various parts and of the materials of which they are formed `may be resorted to as come within the scope of the sub-joined claims.

Having now described the invention so that others skilled in the art may clearly understand the same, what it is desired to secure by Letters Patent is as follows:

1. A switch Vcomprising a casing, a contact member fixed therein, a sleeve of insulating material within said casing, and a, movable Contact member supported thereby for movement toward and from said xed contact member, means resiliently urging said movable contact member into contact with said xed Contact member, said casing having two pressure chambers therein separated by said sleeve and passages for introducing uid under pressure simultaneously into said chambers, whereby variations of fluid pressure within said chambers will open said switch and permit said switch to close.

i, 2. A switch comprising a casing having a chamber therein and a counterbore of smaller diameter than said chamber extending from said chamber to adjacent one end of said casing, a fixed contact member extending through said casing into the closed end of said counterbore, a bushing of insulating material separating the closed end of said counterbore from'said chamber, a movable contact member mounted in said bushing and extending into said counterbore, resilient electrical conducting means urging said movable contact member into contact with said fixed contact member and forming a part of the circuit controlled by said switch, and a passage in said casing opening into said counterbore at the closed end thereof to admit fluid under pressure to said counterbore at the side of said bushing opposite said resilient means to open said contact.

3. In a fiuid pressure actuated cut-out switch, a hollow casing, movable means comprising an electrical contact member and an insulating bushing therefor dividing the interior of said casing into two separate chambers, respective fluid channels leading to said chambers, and a fixed contact member in one of said chambers in electrical contact with said casing and cooperating with said movable contact member to make and break an electrical circuit including said switch, an electrical connector insulatedly carried at one end of said chamber, and a spring urging said contact'l members together and constituting the sole electrical connection between said connector and said movable contact.

4. The arrangement as set forth in claim 3 in which said bushing is dimensioned to provide clearance between itself and said casing to provide a restricted passage for the ow of fiuid from one of said chambers to the other chamber.

5. A fluid pressure actuated electric switch comprising, a unitary casing adapted to be mounted on a machine surface and having at one side thereof a fiat external surf ace and interiorally thereof a bore open at one end and closed at the opposite end and providing tandem pressure chambers, and fluid passages extending one from each pressure chamber and opening to said flat surface, a, fixed contact member mounted in said casing at the closed end of said bore, an insulating bushing slidable in said bore between said fluid passages, and a movable contact member carried by and extending through said bushing.

6. A fluid pressure actuated electric switch comprising, a unitary casing adapted to be mounted on a machine surface and having at one side thereof a flat external surface and interiorly thereof a bore open at one end and closed at the opposite end and providing tandem pressure chambers, and fluid passages extending one from each pressure chamber and opening to said flat surface, a fixed contact member mounted in said casing at the closed end of said bore, an insulating bushing slidable' in said bore between said fiuid passages, and a movable contact member carried by and extending through said bushlng, said contact members constituting 'a stop for said busihng to restrain said bushing from covering the end of one of said fluid passages.

'1. In a fluid pressure actuated switch, a unitary casing comprising a flat plate base portion having a fiat surface, and a cylindrical portion extending across said base portion and provided with an internal bore the axis of which is substantially parallel to said fiat surface and which is closed at one end by the casing wall, a fixed contact member secured in said casing, a plunger in said bore separating said bore into two fluidV chambers each connected through a respective fluid channel with the face surface of said base portion, and a movable contact member carried by said plunger.

8. In a uid pressure actuated switch, a unitary casing comprising -a base portion having a fiat face surface, and a chamber portion having a bore the axis of which is substantially parallel to said face surface and which is closed at one end by a wall of said-casing, a fixed contact member carried by said casing at one end of said bore, means including a movable contact member dividing said bore into separate pressure chambers each connected through a respective fiuid channel with said flat face surface, and a current conducting spring in said bore resiliently urging said movable contact member toward said fixed'contact member.

9. In an oil pressure actuated switch, a casing having a high pressure chamber and a low pressure chamber and an intercommunicating cylinder wall therebetween, a fixed contact in said high pressure chamber, an insulated piston slidable in said cylinder wall and carrying a movable contact, and a spring in said low pressure chamber electrically connected to said movable contact and urging the same into engagement with said fixed contact, said piston being smaller than said cylinder wall and having a clearance to permit passage of oil from said high pressure chamber around and past said piston to said low pressure chamber.

10. In an oil pressure actuated switch, a casing having a high pressure chamber and a low pressure chamber and an intercommunicating cylinder wall therebetween, a fixed contact in said high pressure chamber, an insulated piston slidable in said cylinder wall and carrying a movable contact, and a spring in said low pressure chamber urging said piston toward said fixed contact to maintain said movable contact in engagement therewith, said casing having a passage connected with an actuating system and said high pressure chamber for admitting high pressure oil from the actuating system to said high pressure chamber and another passage connected with said actuating system and said low pressure chamber Vfor returning oil from said low pressure chamber to the actuating system, and said piston being smaller than said cylinder wall and having a clearance for the passage of oil from said high pressure chamber to said low pressure chamber.

11. In an oil pressure actuated switch, a casing having a high pressure chamber and a low pressure chamber, a fixed contact in said high pressure chamber, an insulated piston subject to said high pressure and carrying a movable contact, a spring in said low pressure chamber electrically connected to said movable contact and urging the same into engagement with said fixed contact, said low pressure chamber having an insulated wall, and a terminal carried by said wall forming a seat and a guide for said spring and forming a stop for said movable contact.

12. In an oil pressure actuated switch, a metal casing having a rst bore and a smaller bore extending therebeyond, a fixed contact grounded in said smaller bore, an insulated piston slidable in said smaller bore and carrying a movable contact having a head extending into said first bore, an insulated plug closing said first bore and supporting a terminal stem having a head extending into said first bore, and a. coiled compression metal spring surrounding said terminal head and seated thereon and bearing against the head of said movable contact.

13. A switch forming a portion of a liquid system and comprising a casing having a pressure chamber therein, a fixed contact member extending into said chamber, a second chamber in said casing, a slidable bushing of insulating material separating said chambers and having a. contact member mounted therein and extending into the chamber containing said xed contact, said bushing having clearance in said casing to provide a restricted connection between said chambers, means to admit liquid under pressure from said liquid system to said chamber containing said fixed contact to open said contacts, and means for conducting liquid from said second chamber to said liquid system, some of said liquid under pressure moving through said restricted connection from the contact chamber to said second chamber to prevent an accumulation of sludge and congealing of liquid in said contact chamber.

ERLE MARTIN.

THOMAS E. DOHERTY.

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